Chromosome 11 contains genes which can suppress the tumorigenicity of HeLa cells in nude mice. Suppression of tumorigenicity in HeLa cells was first demonstrated in studies of somatic cell hybrids of HeLa cells with normal human fibroblasts. See, Klinger, Cytogenet. Cell Genet., 27:254-266 (1980) and Stanbridge, Nature, 260:17-20 (1976). These hybrid cell lines, unlike HeLa, were non-tumorigenic, but retained other properties of transformed cells such as immortalization and the ability to grow in soft agar. See, Stanbridge, et al., Science, 215:252-259 (1982). The non-tumorigenic hybrids gave rise to rare segregants which had regained the property of tumorigenicity. Karyotype and RFLP analysis of such segregants demonstrated a loss of one copy of chromosome 11 relative to the non-tumorigenic cell lines. See, Srivatsan, et al., Cancer Res. 46:6174-6179 (1986) and Kaelbling, et al., Cytogenet. Cell Genet., 42:65-70 (1986). Direct functional evidence for the existence of a chromosome 11 HeLa tumor suppressor came with the demonstration that microcell mediated transfer of chromosome 11 to HeLa or a tumorigenic segregant line resulted in partial or complete suppression of tumorigenicity. See, Saxon, et al., EMBO J., 5:3461-3466 (1986). Tumor suppression mediated by chromosome 11 transfer has also been demonstrated in a cell line derived from a Wilms' tumor (see, Weissmann, et al., Science, 236:175-180 (1980)), in the cervical carcinoma cell line SiHa (see, Koi, et al., Mol. Carcinogen., 2:12-21 (1989)), and in a rhabdomyosarcoma cell line (see, Oshimura, et al., J. Cell. Biochem., 42:135-142 (1990)).
The specific chromosome 11 gene or genes responsible for tumor suppression in the HeLa-fibroblast system have not been identified. Comparison of proteins and RNA species expressed by hybrid cell lines has revealed that extremely few genes show differential expression between the tumorigenic and non-tumorigenic hybrids. For example, when 1.2.times.10.sup.5 clones from a subtracted cDNA library were screened, only one differentially expressed gene was identified. See, Dowdy, et al., Nuc. Acids Res., 19:5763-5769 (1991). This gene was expressed at only 2-4 fold higher levels in the non-tumorigenic hybrids than in the tumorigenic segregants. In the HeLa/fibroblast system, one gene which displays marked differential expression has been characterized: that for intestinal alkaline phosphatase (IAP). Both HeLa and the tumorigenic segregants express high levels of this enzyme, whereas virtually no RNA, protein, or enzyme activity is detectable in the suppressed hybrids. See, Latham, et al., Proc. Natl. Acad. Sci. USA, 87:1263-1267 (1990). Although the IAP gene may prove to be a target of the tumor suppressor gene, it does not map to chromosome 11 and does not by itself affect tumorigenicity upon transfection. See, Latham, et at., Cancer Research, 52:616-622 (1992).
A gene which is associated with tumor suppression and is localized on chromosome 11 has now been identified. The identification, localization and sequence of a gene which demonstrates differential expression in a manner that correlates with tumorigenicity suggests that this gene could potentially be used for gene therapy in cancers deleted or altered in their expression of the gene. Furthermore, a gene which is localized on chromosome 11p15, with identified polymorphisms, could be used for analysis of tumor DNA for loss of heterozygosity at chromosome 11p15. This region of chromosome 11 shows frequent loss of heterozygosity (LOH) in many human malignancies. See, Junien, et al., Genomics, 12:620-625 (1992). Thus, the determination of LOH at chromosome 11p15 may be useful in predicting the prognosis of that tumor.